The present invention relates to an exhaust manifold for a vehicle and, more particularly, to an exhaust manifold uniformly distributing exhaust gas passing through the catalytic converter and preventing formation of cracks due to thermal stress.
Generally, the exhaust manifold is the part which collects the exhaust gasses from the respective cylinders of the engine to lead the flow of the collected exhaust gas to an exhaust pipe. In a 4-cylinder engine, usually four runners or pipes are used. In one type, the four runners are directly connected to a gas confluence part that is connected to the catalytic converter and leads to the exhaust pipe and muffler. In another type, the runners are connected in two pairs respectively to the gas confluence part.
The former type (in which the four runners are directly connected) is generally called 4-1 type. In this type first, second, third and fourth runners are connected to a gas confluence part with uniform spacing between the runners at the point they join the confluence part. The gas confluence part is provided with a sensor installation slot for installing an oxygen sensor.
While this type of manifold has a simple structure, the spacing between the runners is narrow where it joins the gas confluence part. As a result, the gas confluence part frequently cracks due to thermal stress, with the result that the overall life of such an exhaust manifold is decreased. An additional drawback exists in that exhaust gas interferences occur between the runners in accordance with the ignition sequence (first cylinderxe2x86x92third cylinderxe2x86x92fourth cylinderxe2x86x92second cylinder).
The second type of manifold (in which the four runners are connected to the gas confluence part in two pairs) is generally called 4-2-1 type. In this type the first and fourth runners are joined together in a Y-shape before being connected to the gas confluence part. Likewise, the second and third runners are joined together in a Y-shape before also being connected to the gas confluence part. As a result, only two passages, i.e., a passage which has been formed by the joining of the first and fourth runners, and another passage which has been formed by the joining of the second and third runners, are connected to the gas confluence part. The gas confluence part is also provided with a sensor installation slot for installing an oxygen sensor.
This 4-2-1 type exhaust manifold has an advantage that the flow of the exhaust gas is more efficient compared with the 4-1 type exhaust manifold. However, in this exhaust manifold, because the first runner and the fourth runner face toward each other, if the length of the first and fourth runners is too short, an exhaust gas interference cannot be avoided in accordance with the igniting sequence (first cylinderxe2x86x92third cylinderxe2x86x92fourth cylinderxe2x86x92second cylinder). As with the 4-1 type exhaust manifold, the spacing between the runners is narrow where they join the confluence part, again resulting in thermal stress cracks.
Further, the 4-2-1 type exhaust manifold is more complicated in its structure compared with the 4-1 type exhaust manifold. Consequently, the manufacture is more difficult and the weight greater
In an embodiment of the present invention, first and fourth runners of an exhaust manifold are respectively directly connected to a gas confluence part, while second and third runners are joined together before connecting to the gas confluence part. With this arrangement, flow of exhaust gas is more efficient in streaming to the gas confluence part, and exhaust gas interference is prevented in accordance with the igniting sequence (first cylinderxe2x86x92third cylinderxe2x86x92fourth cylinderxe2x86x92second cylinder). Also, spacing between the runners is widened at the gas confluence part so as to reduce or prevent formation of cracks due to thermal stress.
In a further preferred embodiment of the present invention, the cross sectional area of the runners at the connection point to the confluence part is expanded, whereby the flow velocity of the exhaust gas is slowed to more uniformly distribute exhaust gas passing through the catalytic converter so as to improve its performance.